[2.0] Fix Failed Jobs page showing no results when failed jobs do exist

[derekmd]

Fixes: #476, #458, #109

I've seen the Failed Jobs section behave like this since the Horizon beta was released.

The Vue component expects its jobs prop to be an Array but the API endpoint can return an object in its JSON body. A filtered PHP associative array needs to be kept as 0-indexed.

horizon/resources/js/pages/Failed/Index.vue

Lines 71 to 73 in 032959e

	this.$http.get('/horizon/api/jobs/failed?' + tagQuery + 'starting_at=' + starting)
	.then(response => {
	this.jobs = response.data.jobs;

#476 (comment) has a longer explanation of what I found. I wasn't able to figure out how to recreate the edge case in a PHPUnit test. Do we have an explanation of where this empty payload is coming from when fetching a set of jobs?

horizon/src/Repositories/RedisJobRepository.php

Lines 193 to 197 in 6db1be6

	return $this->indexJobs(collect($jobs)->filter(function ($job) {
	$job = is_array($job) ? array_values($job) : null;
	return is_array($job) && $job[0] !== null;
	}), $indexFrom);

Does Redis ZRANGE (called in RedisJobRepository@getJobsByType()) sometimes return keys that don't exist? This test attempt didn't seem to indicate that.

[driesvints]

Do we have an explanation of where this empty payload is coming from when fetching a set of jobs?

Not that I know off.

But this is indeed the correct solution. I just tested this and it indeed needs it to be an array at all times. Can you maybe whip up a test that always expects the collection to not be a key-pair value?